1. Field of the Invention
This invention relates to a method for removing hydrogen fluoride (HF) from mixtures comprising HF and aromatic ketones. More specifically, the invention relates to the removal of hydrogen fluoride from mixtures comprising HF and aromatic ketones resulting from the Friedel-Crafts acylation of an aromatic compound with an acyl fluoride, a carboxylic acid anhydride, a free carboxylic acid or a combination of the foregoing acylating agents, using HF as solvent/catalyst.
2. Description of Related Art
The following information is disclosed in accordance with the terms of 37 CFR 1.56, 1.97, and 1.98.
Aromatic ketones which can be produced by Friedel-Crafts acylations using hydrogen fluoride as solvent/catalyst are possible intermediates for a variety of products having a multiplicity of end uses. Thus, U.S. Pat. No. 4,524,217, issued June 18, 1985 to Davenport et al., discloses a process of using hydroxy aromatic ketones, e.g., 4-hydroxyacetophenone (4-HAP), to make N-acyl-hydroxy aromatic amines, e.g., N-acetyl-para-aminophenol (APAP), better known as acetaminophen, which has wide use as an analgesic. U.S. Pat. No. 4,568,763, issued Feb.4, 1986 to Davenport et al., discloses the use of hydroxy aromatic ketones such as 4-HAP as an intermediate for the production of N-acyl-acyloxy aromatic amines, e.g., 4-acetoxyacetanilide (4-AAA), which can be used for the preparation of poly(ester-amide)s capable of forming an anisotropic melt phase and suitable for being formed into shaped articles such as moldings, fibers, and films. In addition, 4-AAA may also be hydrolyzed to form APAP. U.S. Pat. No. 4,692,546, issued Sept. 8, 1987 to Davenport, discloses a process wherein hydroxy aromatic ketones, e.g., 4-HAP, are used to produce acyloxy aromatic carboxylic acids, e.g., 4-acetoxybenzoic acid (4-ABA), which is also capable of being used directly to make polymers which can be formed into an anistropic melt suitable for the formation of shaped articles. Moreover, 4-ABA can be hydrolyzed to 4-hydroxybenzoic acid (4-HBA) which can be used as an intermediate for the production of preservatives, dyes, and fungicides.
The foregoing U.S. patents and pending applications each shows the production of aromatic ketones by the Friedel-Crafts acylation of aromatic compounds with an acylating agent such as an acyl halide, a carboxylic acid anhydride or a free carboxylic acid, using hydrogen fluoride as solvent/catalyst. In addition to these disclosures, U.S. Pat. No. 4,607,125 issued Aug. 19, 1986 to Mott and pending application Ser. No. 714,407, filed Mar. 21, 1985 by Davenport et al., teach processes for the production of 4-HAP by the Friedel-Crafts acetylation of phenol with acetic anhydride utilizing hydrogen fluoride as catalyst and reaction conditions within certain prescribed ranges.
U.S. Pat. No. 4,593,125, issued June 3, 1986 to Davenport et al., shows the acylation of various substituted naphthalenes using an acylating agent such as an acyl fluoride, a carboxylic acid anhydride or a free carboxylic acid and hydrogen fluoride as catalyst to obtain the corresponding substituted naphthones, e.g., 6-hydroxy-2-acetonaphthone (6, 2-HAN).
Japanese Early-Disclosure (Kokai) 85-188343 published Sept. 25, 1985 discloses the preparation of aromatic ketones by reacting an aromatic compound with an acyl fluoride in the presence of hydrogen fluoride, with the acyl fluoride being separately prepared by reacting an acid anhydride with hydrogen fluoride.
U.S. Pat. No. 4,059,633 issued Nov. 22, 1977 to Childs, discloses a process for the recovery of hexafluoroacetone from a hexafluoroacetone-HF complex with acetic anhydride under reaction conditions. The reaction produces liberated hexafluoroacetone and by-products, acetyl fluoride and acetic acid.
Pending application Ser. No. 158,141 filed Mar. 4, 1988 by Elango et al., shows the production of 4-isobutylacetophenone (4-IBAP) by the Friedel-Crafts acetylation of isobutylbenzene (IBB) with an acetylating agent which may be acetyl fluoride (AcF) acetic anhydride (Ac.sub.2 O), using a catalyst which may be hydrogen fluoride. The 4-isobutylacetophenone is disclosed as an intermediate in a process for the production of ibuprofen.
In general, processes for producing aromatic ketones by acylating an aromatic compound with an acyl fluoride, a carboxylic acid anhydride, and/or a free carboxylic acid as acylating agent, utilizing hydrogen fluoride as a catalyst, employ an excess of hydrogen fluoride and acylating agent and result in a product mixture comprising hydrogen fluoride and carboxylic acid if anhydride was used as acylating agent as well as aromatic ketone product. Such mixture must be purified both to obtain aromatic ketone of sufficient purity to make it suitable for further use, and to recover the hydrogen fluoride for recycling to the process. Some of the free, i.e., uncomplexed HF may be removed by straight distillation under relatively mild conditions. However, because of the frequent formation of a stable and relatively high boiling complex of aromatic ketone and HF, and a complex of carboxylic acid and HF if carboxylic acid is present in the mixture, removal of sufficient HF necessary to obtain an aromatic ketone of suitable purity may require distillation under vacuum at temperatures so high as to cause an unfavorable loss of aromatic ketone due to polymerization or other side reactions. Thus, any process which achieves a satisfactory level of separation of HF from the aromatic ketone product and from the carboxylic acid, if present, without undue loss of product, is very desirable.
One method of purification includes an initial solvent-assisted distillation (SAD) of the mixture as disclosed, for example, in U.S. Pat. No. 4,663,485, issued May 5, 1987 to Murphy et al., and pending application Ser. No. 013,311 filed Feb. 11, 1987 by Murphy et al. In this method, a composition comprising an aromatic ketone, e.g., 4-hydroxyacetophenone (4-HAP), and an inorganic fluoride consisting essentially of hydrogen fluoride (HF), is distilled in a column or other vessel in the presence of an assisting solvent which is stable in the presence of HF. The vapor overhead comprises a major portion of the HF in the feed to the distillation vessel mixed with some assisting solvent. A liquid residue containing solvent and most of the aromatic ketone in the feed and which may contain heavy ends other than the desired aromatic ketone, is obtained from the base of the column. When the composition being purified is that resulting from the acylation of an aromatic compound with an acyl fluoride and/or a carboxylic acid anhydride using HF as a solvent/catalyst, and thus contains aromatic ketone, HF, and some carboxylic acid if the anhydride was used as all or part of the acylating agent, then the overhead in the solvent-assisted distillation column will contain HF, assisting solvent, and carboxylic acid if present. After separation of the assisting solvent by decantation or distillation (assuming the assisting solvent is not the carboxylic acid) the composition remaining will comprise HF, and carboxylic acid if present, with possibly a small amount of assisting solvent. However, before recycling HF to the process (a step necessary for economic reasons), the carboxylic acid must be separated or substantially reduced in content since its presence inhibits the acylation reaction due to equilibrium considerations.
While the foregoing solvent-assisted distillation alone is generally effective in reducing the level of HF in the aromatic ketone to a lower level than could be obtained by straight distillation of the mixture at a temperature which does not cause substantial decomposition of the ketone, such an HF level is often still too high for many applications of the aromatic ketone. Furthermore, solvent-assisted distillation, when used as the sole method for reducing the HF in an aromatic ketone to a prescribed level, may have other disadvantages, such as mutual solubility, high cost of equipment, excessive foam formation, and contamination and high energy cost due to the use of large amounts of assisting solvent.